Coherent structures and bubble-particle velocity in 2-D fluidized beds

This work presents an experimental study to characterize ascending bubbles and granular velocity in the dense phase of a 2-D fluidized bed. Three different non-intrusive techniques based on images obtained with a high speed camera are developed, and applied to the images. First the bubble paths are characterized with time-average concentration maps and the bubble velocities are obtained, using a tracking algorithm over the mass centers of the bubbles. Finally, a PIV (particle image velocimetry) method is used to characterize the particle velocity vectors. This procedure is repeated for different bed aspect ratios, and different superficial gas velocities. This study analyzes the superficial gas velocity influence on the bed behavior, and how the bubble path configuration depends on the bed aspect ratio. The PIV measurements give us information on the location of the recirculation regions and the influence of the superficial gas velocity.Publicad

Diseño de partículas a base de inulina de Dalia (Dahlia variabilis Cav.) para la liberación controlada de un extracto de Jamaica (Hibiscus sabdariffa L.)

0La dalia (Dahlia coccinea Cav.) es una planta que ha sido cultivada y mejorada genéticamente con fines ornamentales; no obstante, su sistema radicular almacena carbohidratos de reserva bajo la forma de inulina y otros fructanos. La inulina forma parte de la fibra dietética de diversos vegetales y es considerada como un compuesto prebiótico. Este polisacárido se extrae principalmente de la achicoria y la alcachofa mediante métodos de separación muy variados, siendo la raíz de la dalia una opción interesante de explotación industrial. El propósito de este estudio fue proponer un método simple de extracción de inulina de la raíz de dalia y evaluar el efecto del cultivo de dalias silvestres sobre su contenido de inulina, fructanos, fructosa y glucosa. Se realizaron colectas de dalia silvestre y se propuso un método de extracción de inulina. Las semillas de los ejemplares recolectados fueron cultivadas y a las raíces obtenidas se les determinó la concentración de fructanos, inulina, fructosa y glucosa y se estimó el grado de polimerización. La relación tiempo-temperatura afecta significativamente la concentración de inulina y fructanos extraídos, siendo la combinación óptima 80° C durante 60 minutos. La influencia del pH resultó no significativa para este mismo propósito. Por otro lado, el cultivo de las dalias silvestres aumenta significativamente el contenido de inulina y fructanos de sus raíces, aunque el grado de polimerización, estimado a partir de la relación fructosa/glucosa, disminuye. La liberación de polifenoles encapsulados en inulina en una solución isotónica sigue una cinética de primer orden con una constante de velocidad (basada en la absorbancia del medio isotónico) de 0.0148 unidades por minuto y una liberación máxima de 0.4166 unidades de absorbancia que se observaron a las 8 horas de permanencia de las partículas en la solución isotónica.

Hybrid sol-gel coatings containing clay nanoparticles for corrosion protection of mild steel

The development of a new environment-friendly anticorrosive coating for mild steel substrate is afforded in this work. The combined use of cerium, as a self-healing agent, and clay nanoparticles, as improvers of the barrier properties, was considered to the development of new anticorrosive sol-gel coatings. Nanostructured hybrid films were synthesized by the sol-gel route from tetraethoxysilane (TEOS) and 3-glicidoxipropyl-trimetoxisilano (GPTMS) using laminar nanoclays (Laponite Na+0.7[Si8Mg5.5Li0.3H4O24]−0.7) to improve mechanical and barrier properties, and Ce(NO3)3?6H2O as a supplier of Ce(III) to provide an inhibiting effect in the event of coating failure. Carbon steel plates, AISI 1010, were used as substrates. Prior to the application of the coating, samples were treated with a phosphoric acid 2% v/v in order to improve coating adherence.In order to evaluate cerium effect, electrochemical behaviour of films containing Laponite and cerium salts (TGL-Ce) were compared with films containing only Laponite (TGL) by means of potentiodynamic polarization tests and electrochemical impedance spectroscopy (EIS) measurements using a 0.35 wt% NaCl solution. Microstructural characterization and surface analysis of substrates and sol-gel coatings were performed by optical microscopy and by XPS techniques. The use of nanoclays allowed to achieve a significant improvement of the anticorrosive behaviour of the cerium doped coating at the same time that enhances the physical integrity of the coatings under immersion tests.Fil: Santana, Ianina Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Pepe, Andrés. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Schreiner, Wido H.. Universidade Federal do Paraná; BrasilFil: Pellice, Sergio Antonio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Ceré, Silvia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentin

Exergy Optimization of a Moving Bed Heat Exchanger

The MBHE proposed can be analyzed as a crossflow heat exchanger where one of the phases is a moving granular medium. In the present work the exergy analysis of the MBHE is carried out over operation data of the exchanger obtained in two ways: a numerical simulation of the stationary problem and a simplified analysis. The numerical simulation is carried over the two steady state energy equations (fluid and solid), involving (for the fluid) the convection heat transfer to the solid and the diffusion term in the flow direction, and (for the solid) only the convection heat transfer to the fluid. The simplified analysis followed the well-known e-NTU method, taking the equipment as a crossflow heat exchanger with both fluids unmixed.Publicad

Estimation and experimental validation of the circulation time in a 2D gas-solid fluidized beds

The circulation time is defined as the time required for a group of particles to reach the freeboard from the bottom of a fluidized bed and return to their original height. This work presents an estimation and validation of the circulation time in a 2D gas solid bubbling fluidized bed under different operating conditions. The circulation time is based on the concept of the turnover time, which was previously defined by Geldart [1] as the time required to turn the bed over once. The equation tc,est =2Ah′/Qb is used to calculate the circulation time, where A is the cross section of the fluidized bed, h′ is the effective fluidized bed height and Qb is the visible bubble flow. The estimation of the circulation time is based on the operating parameters and the bub ble phase properties, including the bubble diameter, bubble velocity and bed expansion. The experiments for the validation were carried out in a 2D bubbling fluidized bed. The dense phase velocity was measured with a high speed camera and non intrusive techniques such as particle image velocimetry (PIV) and digital image analysis (DIA), and the experimental circulation time was calculated for all cases. The agreement between the theoretical and experimental circulation times was satisfactory, and hence, the proposed estimation can be used to reliably predict the circulation time.Publicad

A novel approach for modeling bubbling gas–solid fluidized beds

A phenomenological discrete bubble model is proposed to help in the design and dynamic diagnosis of bubbling fluidized beds. An activation region mechanism is presented for bubble formation, making it possible to model large beds in a timely manner. The bubbles are modeled as spherical-cap discrete elements that rise through the emulsion phase that is considered as a continuum. The model accounts for the simultaneous interaction of neighboring bubbles by including the trailing effects due to the wake acceleration force. The coalescence process is not irreversible and therefore, the coalescing bubble pair is free to interact with other rising bubbles originating the splitting phenomena. To validate the model, the simulated dynamics are compared with both experimental and literature data. Time, frequency, and state space analysis are complementarily used with a multiresolution approach based on the empirical method of decomposition to explore the different dynamic scales appearing in both the simulated time series and those obtained from experimental runs. It is concluded that the bubble dynamics interactions play the main role as the driver of the resulting bed dynamics, matching the main features of measured bubble dynamics. Exploding bubble phenomena have been identified by establishing a direct relation between the bubble generation, interaction and eruption, and the measured signalsProjects DPI2009-10518 (MICINN) and CARDENER-CM (S2009ENE-1660)Publicad

Usos de la microscopía electroquímica de barrido (SECM) para la investigación de procesos localizados de corrosión

La microscopía electroquímica de barrido (SECM) es una técnica muy apropiada para el estudio local de los procesos de corrosión debido a que suministra información  insitu, a escalas micrométrica y submicrométrica, relativa a la topografía y a la actividad electroquímica de superficies reactivas en disolución acuosa. La resolución espacial se obtiene en base a desplazar una sonda colocada en la proximidad de la superficie activa, permitiendo la comparación de las respuestas locales en diferentes regiones. En esta comunicación se presentan los modos de operación de la técnica que encuentran aplicación para la investigación de procesos localizados de corrosión, ilustrándose cada uno de ellos con un ejemplo de su aplicación en el laboratorio de corrosión